Automatic focusing apparatus

Abstract

In an automatic focusing apparatus which detects sharpness signals from high-frequency components of brightness signals contained in video signals from video cameras and which stops a focusing lens of the video camera at a position at which its peak value is obtained, the movement of the focusing lens is started by detecting received light signal levels by performing projection-reception operations with a specified amount of infrared light and detecting their variations with a received light signal level detector or with a micro-computer. Furthermore, depending upon the focal depth of the focusing lens, priority is given to processing of distance information based on sharpness signals or distance information determined by the infrared light projection-reception operation in the lens driving controller for performing the focusing operation. According to the automatic focusing apparatus of the present invention, movement of the lens only due to variations of contrasts can be avoided, and stable image pictures are thus obtainable. Also, the most suitable focusing operation mode for a particular focal depth of a lens in use can be selected.

We claim: 
     
       1. An automatic focusing apparatus with a lens movement termination means, comprising: a sharpness signal generation means which detects a sharpness signal from high-frequency components of a brightness signal contained in a video signal corresponding to an object;   a maximum value detection means which generates a lens movement termination signal which stops movement of a focusing lens when said sharpness signal has a peak value;   a distance variation detection means comprising a light projection means which projects a specified amount of infrared light onto said object, a light reception means which receives reflected lights caused by projection of said specified amount of infrared light onto said object, and a received light signal level variation detection means which detects variations of the light level of said reflected infrared light for issuing a lens movement start signal; and   a lens driving means including a driving source for controlling the movement of a lens in response to said lens movement termination signal and said lens movement start signal.   
     
     
       2. An automatic focusing apparatus as claimed in claim 1, wherein said sharpness signal generation means comprises: a color signal elimination circuit which takes out only said brightness signal from said video signal;   a differential circuit which takes out high-frequency components from said brightness signal;   a gate circuit which selects high-frequency components included within a specified region of the picture frame; and   a detection circuit which forms sharpness signals from said high-frequency components obtained through said gate circuit.   
     
     
       3. An automatic focusing apparatus as claimed in claim 1, wherein said maximum value detection means and said received light signal level variation detection means of said distance variation detection means are constituted by a microcomputer which: (1) measures and memorizes first, second, and third signals corresponding to said sharpness signal, said reflected infrared light signal level, and positions of said lens, respectively;   (2) compares a measured value of said second signal at a preceding time with a measured value of said second signal at the present time, and when there is a difference, starting the lens movement toward a specified direction by issuing a lens movement start signal;   (3) compares a measured value of said first signal at a preceding time with a measured value of said first signal at the present time, and when the presence of an increase of the level of said first signal is detected, outputting a fourth signal;   (4) detects the presence of said fourth signal; and   (5) when the presence of said fourth signal is confirmed, issues a lens movement termination signal.   
     
     
       4. An automatic focusing apparatus, comprising: sharpness signal generation means for generating sharpness signals from high-frequency components of a brightness signal contained in a video signal as a first distance information signal;   distance detection means for performing a light projection-reception operation of a specific amount of infrared light onto said object and for outputting a received reflected infrared light signal;   distance information generation means for detecting a level of said received reflected infrared light signal and generating a second distance information signal;   focal depth information generation means for generating focal depth information corresponding to a focal depth of a lens;   a lens driving circuit including a driving source which moves said lens; and   lens driving control means supplied with said first and second distance information signals and said focal depth information for outputting a movement start signal for said lens by detecting variations in said second distance information and selecting based upon said focal depth information a first operation state wherein the focusing state is determined from said first distance information or a second operation state wherein the focusing state is determined from said second distance information, wherein said lens driving control means outputs a movement termination signal to said lens for respectively selected operation states and said movement start signal and said movement termination signal are supplied to said lens driving circuit so as to bring said lens into focus.   
     
     
       5. An automatic focusing apparatus as claimed in claim 4, wherein said lens driving control means includes: a distance variation detection circuit which outputs said movement start signal to said lens when variation of said second distance information is detected;   an operation part having a plural number of operation mode including said first and second operation states; and   a mode selection part which selects said operation modes in reponse to said focal depth information, wherein said first operation state is selected when said focal depth is shallow, and said second operation state is selected when said focal depth is deep, respectively.   
     
     
       6. An automatic focusing apparatus as claimed in claim 4, wherein said first operation state is set by a selection of the first operation mode which outputs the movement termination signal to said lens when a peak value of the sharpness signal is detected. 
     
     
       7. An automatic focusing apparatus as claimed in claim 4, wherein said second operation state is set by a selection of the second operation mode which sets the focused state based upon a distance signal generated before and a distance signal generated after the focused state, said focusing lens stopping at a sharpness signal peak value output point between said before and after positions, wherein a third operation mode is selected to stop the focusing lens at the focused state based upon said before and after distance signals. 
     
     
       8. An automatic focusing apparatus, comprising: sharpness signal generation means for generating a sharpness signal from high-frequency components of a brightness signal contained in a video signal corresponding to an object;   distance detection means for performing a light projection/reception operation of a specific amount of infrared light onto said object and for outputting a received reflected infrared light signal;   lens driving control means supplied with said sharpness signal and said received reflected infrared light signal for detecting variations of the light level of said received reflected infrared light signal and outputting a lens movement start signal which starts movement of said focusing lens when said variations are detected, said lens driving control neans also outputting a lens movement termination signal which stops movement of said focusing lens when said sharpness signal has a peak value indicating that said lens is in focus; and   lens driving means for controlling the movement of a lens in response to said lens movement start signal and said lens movement termination signal.   
     
     
       9. An automatic lens focusing apparatus, comprising: means responsive to a video signal corresponding to an object for generating a sharpness signal;   driving means for moving a focusing lens;   means responsive to variations in object distances for starting operation of said driving means; and   means responsive to said sharpness signal for generating a termination signal at a maximum value of said sharpness signal for terminating operation of said driving means   
     
     
       10. An automatic focusing apparatus as claimed in claim 9, wherein said termination signal generating means comprises maximum value detection means for detecting maximum values in said sharpness signals and outputting said termination signal when said maximum values are detected. 
     
     
       11. An automatic focusing apparatus as claimed in claim 9, wherein said means for starting said driving means and said termination signal generating means comprise a microcomputer which: (1) measures and memorizes first, second and third signals corresponding to said sharpness signal, an object distance variation signal, and positions of said focusing lens, respectively;   (2) compares a measured value of said second signal at a preceding time with a measured value of said second signal at the present time, and when there is a difference, starting lens movement by issuing a lens movement start signal;   (3) compares a measured value of said first signal at a preceding time with a measured value of said first signal at the present time, and when an increase of the level of said first signal is detected, outputting a fourth signal;   (4) detects the presence of said fourth signal; and   (5) when said fourth signal is detected, issues a lens movement termination signal.   
     
     
       12. An automatic focusing apparatus as claimed in claim 9, further comprising: focal depth information generating means for generating focal depth information corresponding to a focal depth of said focusing lens, said focal depth information being inputting to said termination signal generating means.   
     
     
       13. An automatic focusing apparatus as claimed in claim 12, wherein said termination signal generating means is responsive to said focal depth information, said sharpness signal and an object distance variation signal outputted by said driving means starting means for selecting based upon said focal depth information a first operation mode wherein said termination signal is determined responsive to said sharpness signal and a second operation mode wherein said termination signal is determined responsive to said object distance variation signal. 
     
     
       14. An automatic focusing apparatus as claimed in claim 13, wherein said first operation mode is selected when said focal depth is shallow and said second operation mode is selected when said focal depth is deep, respectively. 
     
     
       15. An automatic focusing apparatus as claimed in claim 13, wherein said second operation mode is selected based upon a distance signal generated before and a distance signal generated after a focused state, said focusing lens stopping at a peak value of said sharpness signal occurring between said before and after positions, wherein a third operation mode is selected to stop the focusing lens at the focused state based upon said before and after distance signals.